The present invention relates to an art of a plastic shield enclosure and, more particularly, to an art of a plastic enclosure having an EMI (Electromagnetic interference) shielding function for a personal hand-held-portable phone.
Generally a plastic enclosure section of an electronic equipment has its inner surface applied with a metal film in order to keep a circuit thereof from unnecessary electric wave leakage and electric wave interference. Such a metal film is prepared by using surface treatment techniques including plating, coating, deposition and flame coating.
However, a compact and high density mounted electronic equipment, such as a personal hand-held-portable phone a may have parts which are in danger of causing short-circuit due to small clearances between components of the circuit and the metal film. Such parts are protected through masking treatment or an insulating film application. In case the electronic equipment includes a built-in antenna, the metal film applied in a certain range of the built-in antenna should be removed so as to prevent adverse effects to antenna characteristics.
An example of such an art is disclosed in Japanese Utility Model Application Laid-Open No. 20492 (1991). FIG. 14 shows a cross-sectional view of a plastic enclosure using this prior art.
In the prior art, a first enclosure section 61 formed of an ABS resin covering an electronic component 60 and a second enclosure section 62 formed of a resin covering the first enclosure section 61 are molded in a body through two-color molding. Here, only a surface of the first enclosure section 61 is processed by a metal plating 63.
The above-mentioned prior art effects reduction of the number of components and the thickness of the whole enclosure body.
In the above-mentioned prior art, however, performing surface treatment for the metal film application costs very much. Additionally, masking treatment and the insulating film application are necessary to protect the parts which are in danger of causing short-circuit to the circuit. If the equipment has a built-in antenna, the metal film which has been applied has to be removed so as to prevent adverse effects on the antenna characteristics, thus further adding to the production cost.
There is another type of conventional shield enclosure formed of a conductive resin of a plastic material in which carbon powder or metal powder is dispersed.
In this prior art using the plastic material dispersed with a carbon powder or a metal powder, a decorative coating should be included for improving an appearance thereof, thus adding to the coating cost. If the equipment mounts a built-in antenna, the insulating process becomes troublesome.